When fossil fuels are gasified to produce fuel gases and synthesis gases, the resulting gases have a high CO.sub.2 content and in addition thereto contain H.sub.2 S and organic sulfur compounds and other impurities, such as HCN. When produced from coal, such gases usually also contain unsaturated hydrocarbon which tend to polymerize and are referred to as resinogetic substances, and NH.sub.3.
These gases are mostly produced under pressure and are almost always scrubbed to remove the above-mentioned impurities. It has become conventional in gas-purification technology to scrub the gases with physically absorbing scrubbing agents.
Such a process, in which organic liquids, such as methanol, are used as scrubbing agents, has been described, e.g. in German Pat. No. 935,144.
It is also known to remove impurities from gases by chemical scrubbing.
German Pat. No. 1,145,740, for example, describes a process of scrubbing gases with water under pressure to remove H.sub.2 O and CO.sub.2 from said gases. An ethanolamine, preferably triethanolamine, and a polybasic material acid in which the terminal hydrogen atom has no longer an acid activity, such as phosphoric acid, are added to the aqueous scrubbing liquor in a very small amount, which totals about 0.02-0.2 moles and in which is so selected that the pH value of the scrubbing liquor is slightly below or not in excess of 8.
In another known process, a mixture of organic liquids, such as methanol, with water and amines is used to scrub the gases (Opened German specification -- Offenlegungsschrift -- No. 1,815,1137).
In physical scrubbing processes it is easy to remove the above-mentioned impurities but the regeneration of the scrubbing agent laden with said impurities results in exhaust gases which can be eliminated or destroyed only at high expense and in a difficult manner particularly in view of ecological requirements. Whereas these impurities, which are generally combustible, in the regeneration exhaust gases having in most cases a high CO.sub.2 content can be burnt, this results in combustion gases which have such a high SO.sub.2 content that the problem is not solved by the combustion alone.
The removal of impurities such as HCN, polymerizable hydrocarbons, mercaptans, and NH.sub.3 from gases by chemical scrubbing requires a high expenditure and involves considerable difficulty. Specifically, it is very difficult to regenerate the scrubbing liquor and to recover the chemicals.